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| The Secret Rules Of Sex: The Strange World Of Animal Passions |
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| posted on Sunday, December 02, 2007 |
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THE SECRET RULES OF SEX: THE STRANGE WORLD OF ANIMAL PASSIONS
By Steve Connor
The Independent
November 30, 2007
Original Link
She is supposed to be coy and reserved when it comes to choosing a sexual partner, whereas he is noted for being brazenly pushy, ready to offer his services to any female that comes his way. Yet the normal sexual stereotypes seem to be turned on their head in the case of the African topi, an antelope where the male of the species likes to say "no".
Zoologists have reported extraordinary behaviour during the courtship rituals of the topi of the Masai Mara game reserve in Kenya where some male antelopes have literally had to fight off over-amorous females gagging to be inseminated. Far from being standoff-ish, female topis have exhibited a sexual predatoriness worthy of Russell Brand.
The topi antelope has a mating system based on an open arena of land where the males gather to defend little territories called "leks" where each individual advertises his sexual availability. Female topis show a distinct preference to mate with the males with the most centrally-positioned lek, and competing males fight over these territories the most.
So far, so stereotypical. But sometimes being a male with a central lek can be an exhausting experience. So exhausting that they often find themselves having to turn away familiar females in favour of unfamiliar individuals visiting for the first time.
Jakob Bro-Jorgensen of the Zoological Society of London, who led the study published in Current Biology, said it was extraordinary to see males rejecting female advances so vehemently. It was as if male topis were in the unusual position of having to ration their valuable sperm.
"I was interested to see that in cases where the male antelope was free to choose between females, he deliberately went for the most novel mate, rather than the most high ranking. However, some pushy females were so aggressive in their pursuit of the male that he actually had physically to attack them to rebuff their advances," Dr Bro-Jorgensen said.
Trying to explain the latest skirmish in the battle of the sexes takes some doing. It has long been established in biology that there is a fundamental difference in the strategies of the two sexes. Males are supposed to distribute their sperm far and wide to all comers, whereas females are noted for being more picky over whom they decide to fertilise their precious eggs.
"When biologists talks about the 'battle of the sexes', they often tacitly assume that the battle is between persistent males who always want to mate, and females who don't. However, in topi antelopes, where females are known to prefer to mate with males in the centre of mating arenas, we've found a reversal of these stereotypic sex roles," said Dr Bro-Jorgensen.
When analysing sex strategies in the animal kingdom zoologists like to invoke the notion of economic investment. Males invest little in each sperm cell – which is why sperm are small and exceptionally numerous.
Provided a male does not have to rear all the young he sires, it pays him to distribute his investment far and wide in the hope that some of it will pay off – a bit like doing the lottery many times over.
Females, however, start out with a more substantial investment. Each of her eggs is a relatively valuable commodity that needs to be carefully managed. It would pay her, for instance, to invest even more in terms of time and effort to ensure that her fertilised egg has a good chance of reaching adulthood. This explain why females of so many different species stick around to rear their young – and why they have to be choosy over which male they decide to mate with.
The lek system of mating is not unique to mammals such as topis. Leks are common in birds especially. They are a useful way of letting females play the field and choose the best male, who is usually the one with the most centrally-located lek – a word meaning "to play" in Swedish.
Like the topi, the males of some lek-mating birds, such as the capercaillie grouse, have also been observed to reject females after a bout of over-indulgence with a line of females. "They get shagged out. But the females just go away and come back the next day," said Professor Tim Birkhead of Sheffield University.
So why doesn't the topi female do the same? The answer seems to be because she is only in oestrus for a day or so and cannot afford to risk being barren for the entire breeding season, according to Dr Bro-Jorgensen. "The females have just a single day to ensure that they become pregnant, and preferably with a hotshot male, so they must focus all of their energies into ensuring that males mate with them in that time," he said. "The males, however, must focus on maximising the potential of their sperm to ensure they impregnate as many females as possible. It was not uncommon to see males collapsing with exhaustion as the demands of the females got too much for them," he added.
The topi and the capercaillie exemplify a system of mating called polygyny, where a male mates with more than one female. A lek system of mating is just one expression of polygyny and is a supreme example of female choice – they are free to mate with any male, but are naturally attracted to those that other females find attractive.
A harem system is another form of polygyny. Here males dominate their females and guard them against the advances of other males – examples range from sea lions to gorrillas. Some polygynous species are also territorial, where defending a resource-rich plot of land brings in females as an added bonus.
The other form of polygamy is polyandry, when a female has more than one male as a mate. Although this is rare, it is not unheard of. One of the best examples is the dunnock, or hedge sparrow, where females can have two "husbands" at the same time to help rear their young.
Nick Davies, a zoologist at Cambridge University, has shown that this system favours females because they can rear more young with two mates. The males probably don't like it much because they have to compete for access to the female. Indeed, Dr Davies has shown that a male dunnock that is not allowed frequent-enough access to his shared "wife" with not feed the resulting offspring.
Straight monogamy is more common, but even here it is not always what it appears to be. Since DNA fingerprinting was invented some 20 years ago, biologists have discovered that supposedly monogamous species engage in sneaky extra-marital sex – or what is termed extra-pair copulations.
DNA studies of offspring have shown that socially monogamous birds ranging from blue tits to albatrosses are not sexually monogamous. Both males and females go for "extra-marital" sex. Only a few species, such as the mute swan, the capricorn silvereye (a songbird) and the California mouse, are truly monogamous – both socially and sexually, Professor Birkhead said.
Which only goes to show, that everything is not what it often seems, especially when it comes to the sexual games animals play. As Dr Bro-Jorgensen said: "We should not regard coyness as the only natural female sex role just as we should not expect that it is always the natural male sex role to mindlessly accept any mating partner. Nature favours a broader range of sex roles." Tell that to Russell Brand.
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PROMISCUITY
Some animals do not conform to any mating system and engage in frequent sex with many partners. The most famous example is the pygmy chimp, or bonobo, where both sexes copulate frequently to ease social tensions within the group. Other promiscuous species include the buffalo weaver and the vasa parrot of Madagascar, whose females mate with a number of males – which she attracts by singing at the top of a tree. She benefits by rearing a clutch of chicks with different fathers – and so with a wider genetic variation.
MONOGAMY
Swans
Few species are truly monogamous, but mute swans not only mate for life, they are sexually faithful. Both sexes help to rear their young and the male can be assured that the offspring are his, and not those of another male. Monogamy is an advantage when both parents are needed to rear a brood.
Bluetits
Socially monogamous, ie, they act as if they are involved in an exclusive pair bond, but genetic testing shows that often the offspring are the result of "extra-marital" sex. Females as well as males engage in this form of limited promiscuity.
Sea horses
Occasionally there is a complete role reversal in nature when it comes to the sexes. In an extreme form of male monogamy, the male sea horse gets "pregnant" when the female's eggs are embedded in him. He fertilises them and gives birth to live young.
POLYGAMY
Topis
This species of antelope uses a "lek" system of polygynous mating, where males compete with one another in an open arena with the best, most attractive male occupying territories, or leks, at the centre of the arena. The males with the most centrally-placed leks are viewed as the most sexually attractive –and can soon get exhausted by libidinous females. Biologists have observed that these males often turn down mating opportunities, which is rare in the animal kingdom.
Sea lions
Another form of polygyny is the harem system of mating. Here a dominant male defends his females against the attentions of other males. He has to fight his way to this position and has to keep fighting to retain it. The reproductive benefits of winning – and the costs of losing – are immense, which is why the fights can be vicious.
Dunnock
Practises polyandry, ie, the female has more than one mate. The female dunnock often has two "husbands" in a ménage à trois that favours her more than the males. She can ear more offspring this way, but the trade-off is that she had to treat her male companions fairly.
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NHNE Male/Female/Relationship Research
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